P-GLU-D-PHE-TRP-SER-TYR-D-PGL-LEU-ARG-PRO-GLY-NH{HD 2 {B and intermediates

ABSTRACT

D-Phe2-D-Pgl6-LRF, is described as well as its synthesis by solid phase techniques and novel intermediates formed by such synthesis. This novel decapeptide exhibits anti-ovulatory activity in mammals.

United States Patent McKinley et al.

[ 1 May 27, 1975 P -GLU-D-PHE-TRP-SER-TYR-D-PGL-LEU- ARG-PRO-GLY-NH AND INTERMEDIATES Inventors: Wayne A. McKinley, Wallingford;

Dimitrios Sarantakis, West Chester, both of Pa.

Assignee: American Home Products Corporation, New York, NY.

Filed: Apr. 10, 1974 Appl. No.2 459,513

US. Cl 260/112.5; 424/177 Int. CL. C07c 103/52; C07g 7/00; A6lk 27/00 Field of Search 260/ 112.5 LH

References Cited OTHER PUBLICATIONS Yanaihara et al., Biochem. Biophys. Res. Comm, 52, 64-73 (I973).

Primary ExaminerLewis Gotts Assistant ExaminerReginald J. Suyat [5 7] ABSTRACT 5 Claims, No Drawings 1 P-GLU-D-PHE-TRP-SER-TYlR-D-PGL-LEUARG- PRO-GLY-NH AND INTERMEDIATES This invention relates to the novel decapeptide p- Glu-D-Phe Trp-Ser-Tyr-D-Pgl-LewArg-Pro-Gly-NH its process of manufacture and novel intermediates formed in such synthesis.

The luteinizing hormone releasing factor (hereafter called LRF) is the decapeptide, L-(5-oxoprolyl)-L- histidyl-L-tryptophyl-L-seryl-L-tyrosyl-glycyl-L-leucyl- L-arginyl-L-prolyl-glycine amide. See Matsuo, et al., Biochem. and Biophy. Res. Comm. 46, pp l,334-l ,3 39 (l97l This decapeptide is secreted by the hypothalamus and carried to the adenohypophysis where it stimulates the release of the luteinizing hormone and the follicle stimulating hormone The present invention concerns itself with structural modifications of LRF in which the amino acid in the two position (i.e. His) is replaced by D-Phe and glycine in the six position of the peptide chain replaced by D-phenylglycine.

The novel peptides of the present invention are represented by the compounds of the formula:

p-Glu-D-Phe-Trp-Ser-Tyr-D-Pgl-Leu-ArgPro-Gly- NH2 and its non-toxic acid addition salts. The abbreviation Pgl stands for C-Phe.Gly or Cphenylglycine. All chiral amino acid residues identified in formula 1 supra, and the other formulas hereinafter are of the natural or L-configuration unless specified otherwise.

Also contemplated within the scope of the present invention are intermediates of the formula Arg(N"'-R)-Pro-Gly-X (ll) wherein:

N means the side chain nitrogen atoms of arginine;

R is a protecting group for the N N and N" nitrogen atoms of arginine selected from the (III) group consisting of nitro, tosyl, benzyloxycarbonyl, adamantyloxycarbonyl and tert-butyloxycarbonyl; or R is hydrogen which means there are no protecting groups on the side chain nitrogen atoms of arginine. Where the protecting group is nitro or tosyl, the protection is on either one of the N N nitrogens and in the case of benzyloxycarbonyl, or adamantyloxycarbonyl, the protection is on the N nitrogen and either one of the N N nitrogen atoms;

R is a protecting group for the phenolic hydroxyl group of tyrosine selected from the group Consisting of tetrahydropyranyl, tert-butyl, trityl, benzyl, 2,6 dichlorobenzyl, benzyloxycarbonyl ycarbonyl. The preferred protecting group is 2,6- dichlorobenzyl or benzyl; or R is hydrogen which means there is no protecting group on the phenolic hydroxy function;

R is a protecting group for the alcoholic hydroxyl group of serine and is selected from the group consistmg of acetyl, benzoyl, tetrahydropyranyl, tert-butyl, triand 4-bromobenzylox-.

tyl, benzyl. 2,6-dichlorobenzyl or R is hydrogen which means there is no protecting group on the alcoholic oxygen atom. Preferably R is benzyl;

R is preferably hydrogen but may also be an a'amino protecting group. The a-amino protecting group contemplated by R are those known to be useful in the art in the step-wise synthesis of polypeptides. Among the classes of a-amino protecting groups covered by R are (l) acyl type protecting groups illustrated by the following: formyl, trifluoroacetyl, toluenesulfonyl (tosyl), nitrophenylsulfenyl, etc.; (2) aromatic urethan type protecting groups illustrated. by benzyloxycarbonyl and substituted benzyloxycarbonyl such as p-chlorobenzyloxycarbonyl, pnitrobenzyloxycarbonyl, p-bromobenzyloxycarbonyl, p-methoxybenzyloxycarbonyl; (3) aliphatic urethan protecting groups illustrated by tert-butyloxycarbonyl, diisopropylmethoxycarbonyl, isopropyloxycarbonyl, allyloxycarbonyl; (4) cycloalkyl urethan type protecting groups illustrated by cyclopentyloxycarbonyl, adamantyloxycarbonyl. cyclohexyloxycarbonyl and d-isobornyloxycarbonyl; (5) thio urethan type protecting groups such as phenylthiocarbonyl; (6) alkyl type protecting groups as illustrated by triphenylmethyl ('trityl), benzyl; (7) trialkylsilane groups such as trimethylsilane. The preferred a-amino protecting group defined by R are selected from the class consisting of benzyloxycarbonyl, tertbutyloxycarbonyl, tert-amyloxycarbonyl and d-isobor nyloxycarbonyl; In formula II at least one of R, R or R is a protecting group.

X is selected from the group consisting of Nl-l OH, O (lower)alkyl in which (lower) alkyl is C 1 through C (e.g., methyl, ethyl, pentyl, isopropyl, hexyl, etc.), O-benzyl and an anchoring bond used in solid phase peptide synthesis linked to a solid polystyrene resin support represented by one of the formulas:

and

The polystyrene resin support is preferably a copolymer of styrene with about 1 to 2% divinyl benzene as a cross linking agent which causes the polystyrene polymer to be completely insoluble in most organic solvents. The polystyrene polymer is composed of long alkyl chains bearing a phenyl ring on every second carbon and the terminal amino acid residue (Gly) is joined through a covalent carbon to nitrogen or oxygen bond to these phenyl rings. The alkyl chains are cross linked at approximately every fiftieth carbon by p-substituted phenyl residues derived from divinyl benzene. In formula (Ill) the symbol d) means phenyl.

In selecting a particular side chain protecting grour to be used in the synthesis of the peptides of formula: (I) and (II), the following rules should be followed: (a the protecting group must be stable to the reagent am under the reaction conditions selected for removing th a-amino protecting group at each step of the synthesis (b) the protecting group must retain its protectin properties (i.e. not be split off under coupling cond tions), and (c) the side chain protecting group must be removable upon the completion of the synthesis containing the desired amino acid sequence under reaction conditions that will not alter the peptide chain.

Illustrative of pharmaceutally acceptable, non-toxic salts of formula I are hydrochloride, hydrobrommide, sulfate, phosphate, maleate, acetate, citrate, benzoate, succinate, malate, ascorbate, and the like.

The decapeptides of formulas (I) and (II) are prepared using solid phase synthesis. The synthesis is commenced from the C-terminal end of the peptide using an a-amino protected resin. Such a starting material can be prepared by attaching an a-amino protected glycine to a benzhydrylamine resin, a chloromethylated resin or a hydroxymethyl resin, the former being preferred. The preparation of benzhydrylamine resin is described by P. Rivaille, et al., Helv. 54, 2772 (1971) and the preparation of the hydroxymethyl resin is described by Bodanszky, et al., Chem. Ind (London) 38, 1597-98 (1966). A chloromethylated resin is commercially available from Bio Rad Laboratories Richmond, Calif. and the preparation of such a resin is described by Stewart, et al., Solid Phase Peptide Synthesis (Freeman and Co. San Francisco 1969), Chapter I, pp 1-6. In using the benzhydrylamine resin an amide anchoring bond is formed with the a-amino protected glycine as follows:

This permits the C-terminal amide function to be obtained directly after the amino acid sequence in the synthesis is complete by cleaving off the resin support to form the glycine amide at the C-terminal portion of the desired peptide of formula (I). When the other resins are used, the anchoring bond is the benzylester group as defined supra in formula (IV), which after cleavage of the peptide from the resin support must be converted to the C-terminal amide. The preferred procedure is to ammonolyse the protected peptide off the resin and then remove the protecting group by hydrogenolysis or by hydrogen fluoride cleavage. An alternate procedure would be to cleave by transesterification with methanol/(Et) N and then convert the resulting ester into an amide and subsequently deprotect as described above. See .I. M. Stewart Solid Phase Peptide Synthesis, pg. 42-46 (Freeman and Co. San Francisco 1969).

The oz-amino protected glycine is coupled to the ben- :hydrylamine resin with the aid of a carboxyl group acivating compound such as diisopropylcarbodiimide. ollowing the coupling of the a-amino protected glyine to the resin support, the a-amino protecting group removed such as by using trifluoroacetic acid in dihloromethane, trifluoroacetic acid alone or I-ICI in dixane. The deprotection is carried out at a temperature etween about C and room temperature. Other stanard cleaving reagents and conditions for removal of )ecific a-amino protecting groups may be used as de- :ribed in Schroder and Lubke, The Peptides, l Z-75 (Academic Press 1965). After removal of the amino protecting group the remaining a-amino protected amino acids are coupled stepwise in the desired order to obtain a compound of formula (I). However, as an alternate to adding each amino acid separately to the reaction, some of them may be coupled prior to addition to the solid phase reactor. Each protected amino acid or amino acid sequence, is introduced into the solid phase reactor in about a four-fold excess and the coupling is carried out in a medium of dimethylformamide: dichloromethane (1:1) or in dimethylformamide or dichloromethane alone. In cases where incomplete coupling occurred the coupling procedure is repeated before removal of the a-amino protecting group, prior to the coupling of the next amino acid to the solid phase reactor. The success of the coupling reaction at each stage of the synthesis is monitored by the ninhydrin reaction as described by E. Kaiser, et al., Analyt. Biochem, 34, 595 (1970).

After the desired amino acid sequence has been synthesized, the peptide is removed from the resin support by treatment with a reagent such as hydrogen fluoride which not only cleaves the peptide from the resin but also cleaves all remaining side chain protecting groups and the a-amino protecting group (if present) on pyroglutamic acid to obtain directly a compound of formula I in the case where the benzhydrylamine resin was used. Where a chloromethylated resin is used the peptide may be separated from the resin by methanolysis after which the recovered product is chromatographed on silica gel and the collected fraction subject to ammonalysis to convert the methyl ester to the C-terminal amide. Any side chain protecting group may then be cleaved as previously described or by other procedures such as catalytic reduction (e.g., Pd on C) using conditions which will keep the Trp moiety intact. When using hydrogen fluoride for cleaving, anisole is included in the reaction vessel to prevent the oxidation of labile amino acid (e.g., tryptophan).

The solid phase synthesis procedure discussed supra is well known in the art and has been essentially described by M. Monohan, et al., C. R. Acad. SCi, Paris, 273, 508 (1971).

The nomenclature used for peptides is described by Schroder and Lubke, supra, pp viii-xxix and in Biochemistry 11, 1726-1732 (1972).

The following examples are illustrative of the preparation of the compounds of formulas I and II.

EXAMPLE 1 L-pyroglutamyl-D-phenylalanyl-L-tryptophyl-O- benzyl-L-seryl-O-Z,6-dichlorobenzyl-L-tyrosyl-D- phenylglycyl-L-leucyl-N -tosyl-L-arginyl-L-prolylglycyl benzhydrylamine resin.

Benzhydrylamine hydrochloride resin (3 g) in a Merrifield vessel is treated with trifluoroacetic acid (two times, for 5 minutes each), washed with methylene chloride (two times) and dimethylformamide (two times), neutralized with 15% triethylamine in dimethylformamide (two times, for 10 minutes each) and washed with methylene chloride (four times), methanol (three times), and methylene chloride, again (three times). A solution of t-Boc-glycine (0.79, 4.5 m moles) in methylene chloride and dimethylformamide (10:1) is added to the vessel and shaken for 15 minutes. Diisopropylcarbodiimide (0.72 ml, 4.5 m moles) is added next, and the mixture shaken at ambient temperature for 5 hours. The reaction mixture is filtered, washed with methylene chloride, and the vessel recharged in the above manner with t-Boc-glycine and diisopropylcarbodiimide. Twenty hours later, the reaction mixture is filtered and washed with methylene chloride, dimethylformamide, 15% triethylamine in dimethylformamide, dimethylformamide, methylene chloride (three times), methanol (two times), and methylene chloride (three times), and a sample is dried in vacuo. The resin is found to be substituted to the extent of 0.30 m moles of t-Boc-glycine per gram of resin.

The following amino acid residues are introduced onto the above resin consecutively: t-Boc-L-proline (4.5 m moles), t-Boc-N-tosyl-L-arginine (2.3 m moles), t-Boc-L-leucine (2.3 m moles), t-Boc-D- phenylglycine (3.0 m moles), t-Boc-O-2,6- dichlorob'enzyl-L-tyrosine (3.0 m moles), t-Boc-O- benzyl-L-serine (3.0 m moles), t-Boc-L-tryptophan (3.0 m moles), t-Boc-D-pheny1alanine (4.0 m moles), and L-pyrogulatamic L-pyroglutamic (4.0 m moles). All the couplings are carried out in a mixture of methylene chloride and dimethylformamide (3:1) for 18 hours at ambient temperature using a excess of diisopropylcarbodiimide, which is added in two portions over a one hour period. Each coupling is then effected a second time, after filtering and washing with methylene chloride, using one half the original quantities of reactants and allowing a reaction time of 3 hours. The washings between couplings are the same as those described above after the coupling of t-Bocglycine. The deprotection and neutralization is carried out as follows: (a) 1:1 methylene chloride and trifluoroacetic acid (two times for 7 minutes each); (b) methylene chloride; (0) dimethylformamide; (d) triethylamine in dimethylformamide (two times for 7 minutes each); (e) dimethylformamide (two times); (f) methylene chloride; (g) methanol (two times); (h) methylene chloride (three times). The only exception is the use of 5% ethanedithiol in the methylene chloride and trifluoroacetic acid deprotection mixture from the deblocking of the tyrosine moiety on through the remainder of the deprotections.

The washed resin is dried in vacuo overnight.

EXAMPLE 2 L-pyroglutamyl-D-phenylalanyl-L-tryptophyl-L-seryl- L-tyrosyl-D-phenylglycyl-L-leucyl-L-arginyl-L-prolylglycinamide.

EXAMPLE 3 Purification and characterization of L-pyroglutamyl-D-phenylalanyl-L-tryptophyl-L-seryl- L-tyrosyl-D-phenylglycyl-L-leucyl-L-arginyl-L-prolylglycinamide.

The above titled crude product from Example 2 is purified and characterized as follows:

1.37 g of this product in 5 ml of 0.5 N acetic acid is applied to a column (2.5 cm in diameter and 90 cm in height) with a bed of Sephadex G-25F previously equilibrated with 0.5 N acetic acid and eluted with that solvent. Fractions of 4 ml each are taken and analysis of the column effluent is carried out by use of the Folin- Lowry color reaction on every third fraction. Five main peptide containing fractions are obtained: (A) -124 (42 mg), (B) -139 (44 mg) (C) -159 (37 mg), (D) -179 (19 mg) (E) -200 (16 mg). Fractions B, C, D, and E (116 mg) are shown by thin layer chromatography system BWAP (4:2: 1:1) N-butanol:water:acetic acidzpyridine) to contain the same major material. They are combined and applied in 1 ml of the upper phase of n-butanol:0.l M ammonium acetate (1:1) to a column (1.9 cm in diameter and 30 cm in height) with a bed of Sephadex Ll-l-20 previously equilibrated with first the lower phase of nbutanol:0.l M ammonium acetate 1:1 and then with the upper phase of that system. The column is eluted with the upper phase and fractions of 0.5 ml each are taken. The column effluent is monitored as described before. Four major fractions are obtained: (A) 35-49 (12 mg), (B) 50-64 (21 mg), (C) 65-79 (26 mg), (D) 80-100 (23 mg). Fraction A is homogenous by thin layer chromatography system BWAP (422:1 :1 on silica gel (R 0.68). This layer chromatograms are visualized by chlorine peptide reagent, Sacaguchis Reagent, and Paulys Reagent.

After hydrolysis of the peptide in 6 N HCl containing 4% thioglycolic acid for 20 hours at 110C in a closed system under nitrogen, the following values for the amino acid residues are obtained: Glu 1.06; Phe 0.98; Trp 0.24; Ser 1.06; Tyr 1.11; Pgl 0.96; Leu 0.94; Arg 1.04; Pro 0.94; Gly 1.00.

In vivo tests were conducted with female rate (225 to 250 grams body weight). Ovulation inhibition was achieved in the rats tested at a dose of about 24 mg/kg. The test was conducted with mature Sprague-Dawley rats, unanesthetized, proestrous rats. On the afternoon of proestrous, each rat in the test group received six subcutaneous injections of the acetate salt of formula I in corn oil, each injection being given a half hour following the previous injection. The rats are sacrificed the next morning and the number of animals ovulating and the number of ova shed are recorded following the procedure described by E. S. France, Neuroendocrinology 6, pp 77-89 (1970). The absence of or a signicant decrease in the number of ova is the criterion for an antiovulation effect. At a dose of 1 mg per injection complete inhibition of ovulation was achieved.

The compounds of formula 1 can be administered to mammals intravenously, subcutaneously, intramuscularly or orally for fertility inhibition and ovulation control. The effective dosage will vary with the form of administration and the particular species of mammal to be treated. A typical dosage is a physiological saline solution containing a compound of formula 1 administered in a dose range of between about 20 to 30 mg/kg of body weight. Oral administration may be in either solid or liquid form. If the active ingredient is administered in tablet form the tablet may contain: a binder such as gum tragacanth, corn starch, gelatin. an excipient such as dicalcium phosphate, a disintegrating agent such as corn starch, alginic acid, etc.; a lubricant such as magnesium stearate; and a sweetening and/or flavoring agent such as sucrose, lactose, Wintergreen, etc.

What is claimed is:

l. A compound selected from the class consisting of Arg-L-Pro-Gly-NH (l) Pgl-L-Leu-L-Arg(N-R)-L-Pro-Gly-X (ll) and non-toxic acid addition salts thereof; wherein R is a protecting group for the N N and N nitrogen atoms of arginine selected from the group consisting of nitro, tosyl, benzyloxycarbonyl, adamantyloxycarbonyl and tertbutyloxycarbonyl or R is hydrogen;

R is a protecting group for the phenolic hydroxyl wherein said polystyrene resin is cross linked through the phenyl group on each second carbon atom of the alkyl chain of said polystyrene; with the proviso that at least one of R. R and R is other than hy- 5 drogen and wherein Pgl means C phenylglycyl.

2. A compound according to formula ll of claim 1 wherein X is NH 3. A compound according to formula ll of claim 1 wherein R is hydrogen and X is group of tyrosine selected from the group consistl0 P ystyrene resln support and 4. A compound according to claim 3 wherein R is tosyl, R is 2,6-dichlorobenzyl and R is benzyl.

5. A compound according to claim 1 which is selected from L-pyroglutamyl-D-phenylalanyl-L- tryptophyl-L-seryl-L-tyrosyl-D-C-Phenylglycyl-L- leucyl-L-arginyl-L-prolyl-glycinamide and its nontoxic acid addition salts.

. P y- O CH styrene 2 resln support 

1. A COMPOUND SELECTED FROM THE CLASS CONSISTING OF L-P-GLU-D-PHE-L-TRP-L-SER-L-TYR-D-PGI-L-LEU-L-ARG-LPRO-GLY-NH2, (I) R4-L-P-GLU-L-D-PHE-L-TRP-L-SER(R3)-L-TYR(R2)-D-PGL-LLEU-L-ARG(NG-R1)-L-PRO -GLY-X (II) AND NON-TOXIC ACID ADDITION SALTS THEREOF, WHEREIN R1 IS A PROTECTING GROUP FOR THE N, N AND N NITROGEN ATOMS OF ARGININE SELECTED FROM THE GROUP CONSISSTING OF NITRO, TOSYL, BENZYLOXYCARBONYL, ADAMANTYLOXYCARBONYL AND TERT-BUTYLOXYCARBONYL OR R1 IS HYDROGEN, R2 IS A PROTECTING GROUP FOR THE PHENOLIC HYDROXYL GROUP OF TYROSINE SELECTED FROM THE GROUP CONSISTING OF TERT-BUTYL, TETRAHYDROPYRANYL, TRITYL, BENZYL, 2,6-DICHLOROBENZYL, P-BROMOBENZYLOXYCARBONYL AND BENZYLOXYCARBONYL OR R2 IS HYDROGEN, R3 IS A PROTECTING GROUP FOR THE ALCOHOLIC HYDROXYL GROUP OF SERINE AND IS SELECTED FROM THE GROUP CONSISTING OF ACETYL, BENZOYL, TETRAHYDROPYRANYL, TERT-BUTYL, TRITY, 2,6DICHLOROBENZYL AND BENZYL OR R3 IS HYDROGEN R4 IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN OR AN A-AMINO PROTECTING GROUP, X IS SELECTED FROM THE GROUP CONSISTING OF NH2, OH, O(LOWER)ALKYL, O-BENZYL AND AN ANCHORING BOND LINKED TO A SOLID POLYSTYRENE RESIN REPRESENTED BY ONE OF THE FORMULA
 2. A compound according to formula II of claim 1 wherein X is NH2.
 3. A compound according to formula II of claim 1 wherein R4 is hydrogen and X is
 4. A compound according to claim 3 wherein R1 is tosyl, R2 is 2, 6-dichlorobenzyl and R3 is benzyl.
 5. A compound according to claim 1 which is selected from L-pyroglutamyl-D-phenylalanyl-L-tryptophyl-L-seryl-L-tyrosyl-D-C -Phenylglycyl-L-leucyl-L-arginyl-L-prolyl-glycinamide and its nontoxic acid addition salts. 